Control system for paper machines



Jan. 4,,1944. w. H. FORMHALS 2,338,503

CONTROL SYSTEM FOR PAPER MACHINES Filed Jan. 2, 1943 Patented Jam 4,1944

CONTROL SYSTEM FOR PAPER MACHINES William H. Formhals, Forest Hills,Pa., assignor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application lanuaryz1943, Serial No. 471,143

10 Claims.

This invention relates to a control system, and more particularly to animproved arrangement of a control system in paper making apparatus forpreventing sag back upon breakage of the paper between the last set ofdrier rolls and the calender rolls, or similar applications.

In some forms of paper making apparatus, the paper is maintained undertension between the last set of drier rolls and the calender rolls. Inso doing, the motor driving the calender rolls is'caused to take up partof the load necessary to drive the last set of drier rolls. In otherwords, a part or more of the power than is necessary to drive the lastset of drier rolls is furnished by the drive for the calender rolls,

the amount of power being thus furnished being dependent upon the amountoi tension in the strip of paper between the drier rolls and thecalender rolls. In such apparatus the drier rolls and calender rolls areconnected to direct-current machines, and where power is being suppliedto the drier rolls from the calender rolls through tensioning of thepaper, the direct current machine connected to the drier rolls willsupply only a portion of the power or be overhauled and operated as agenerator.

In such case, ity is necessary to strengthen the field on the directcurrent machine connected to the drier rolls in order to maintain theother than the drive for the calender rolls if "sag back" is tobeprevented. This is accomplished by weakening the field on the direct'currentmachine connected to the drier rolls' in such manner as to causeit to take up the load on the drier rolls. However, electricalpaper'mill drives thus far have been found defective in that theregulating apparatus for termined speed, this time delay or sluggishnessof speed regulating systems heretofore available resulted in a slowingdown of the last drier roll set and the formation of a loop or sag back"'of the paper being fed to the last drier: roll set. The "sag back" oithe paper results in the formation of wrinkles and creases in the paperas it is subsequently fed through the last drier roll set. Suchwrinklesare effective not only to deteriorate the;paper being made, butalso result in weakening the same with further breakage between thecalender rolls and drier rolls after subsequent rethread- 'ing of thepaper through the calender rolls.

One of theprincipalobjects of this invention is to provide an improvedarrangement of control apparatus for paper mill equipment which will beeffective to prevent the so-called sag back of paper in front of thelast drier roll set in the event of breakage of the paper in front ofthe calender roll set.

A further object of this invention is to pro- 'vide generator meansintermediate the direct current drive motor for the calender rolls and adynamo connected to the last set of drier rolls which is responsive tothe operating conditions of the calender drive motor for eiiectingproper regulation of the drier roll dynamo with a minimum of time delay.

A further object of this invention is to provide a constant speedgenerator between the direct current machines connected to the cal-vender and drier roll sets of paper mill equipment, together with meansfor rendering 'the output of each generator responsive to the operatingconditions of the calender drivemotor description taken in connectionwith the accontrolling the speed of operation or the varv ious rollsetsrequired a certain amount of time to change the characteristics ofthe direct current machine connected to the drier rolls in such manneras to cause it to take up the load on the drier rolls in the event ofbreakage of'the paper between the drier and calender roll sets. Sincethe paper is delivered companying drawing, in which:

Figure 1 is a diagrammatic showing of paper 'mill equipment having aspeed regulating control system constructed in accordance with V theprinciples of this invention; and

Fig. 2 is a partial view of a part of the con- .trol apparatus shown inFig. 1 showing a rectifier for controlling the direction of current flowin the armature circuit of the speed regulating generator.

Referring to the drawing, the numeral l desto the last drier roll set ata constant predeignates, as a whole, the last set of drier rolls and thenumeral 2 designates, as a whole, a set of calender rolls. A strip ofpaper 3 is shown reeled around the rolls of a drierroll set and threadedthroughthe-stack of rolls in the calender roll set. A dynamo 4 is shownmechanically connected to the drier roll set, and a motor 5 is providedfor driving the calender roll set 2. The paper is fed to the drier rollset I at a constant rate of speed from roll sets (not shown) precedingthe drier roll setgi in a manner customary in apparatus of this kind. Aspointed out above',the paper 3 intermediate the roll sets I and 2iscommonly maintained under tension and motor 5 is thus effective toprovide part of, all of, or more than, the power for operating the drierroll set I. In case the motor 5 supplies more power than necessary tothe drive roll.

set I, generator machine 4 operates as a braking on the drier rolls. Theparts thus far described, including the mechanical connections of thedirect current machines 4 and 5 to, and the mountings of, the roll setsI and 2 form no part per se of this invention, this invention beinglimited to the control apparatus for the direct current machines 4 and5. It willbe understood that such control apparatus is used inconnection with the conventional speed regulating devices (not shown)normally employed for matching the speeds of the various roll sets.

With respect to the novel features of this invention, the strip of paper3 intermediate the roll sets i and 2 may be regarded as a, couplingmeans by which power is delivered from the calender roll set 2 to thedrier roll set i.

The operation of the dynamo 4 is controlled by the direct current motor5 through a generator 6 driven by a constant speed alternatingcurrent'mach ine 'I. 'The output of the generator 6 is controlled bymeans of a field 8 connected in series with the armature circuit of themotor 5, a shunting resistor 9 being provided for limiting the amount ofcurrent fiow through the field 8. The field 8 is arranged in buckingrelation to a field Ill connected to a constant source of potentialsuchas the buses ii and I2.

A control field 13 for the dynamo 4 is connected in series with thearmature circuit of a generator 6. The remainder of the excitation forthe dynamo 4 is provided by a field I4 connected to the constantpotential buses II and I2. Excitation for the motor 5 is provided by afield I5 likewise connected to the buses II and I2. The armatures of themachines 4 and 5 are connected to a source of variable voltage supplysuch as the buses I6 and I! to which the armatures of the other drivemotors (not shown) for the remainder of the paper mill equipment (notshown) are also connected.

The remainder of the control apparatus shown in Figll comprises variableresistors I8, I9 and 20, respectively connected in the circuits of thedynamo field I4, generator field I0, and motor field I5, together withvariable resistors 2I and 22 respectively connected in'the circuits ofthe variable control field I3 and the variable generator field 8.

The number of ampere turns in the generator field III is selected to benormally greater than the number in the variable generator field 8;

Since it will be recalled that the variable field 8 is arranged to buckthe constant field II), it will be apparent that the total field on, andthereby the outputof the generators B, will decrease as the load takenby the motor 5 increases. As the load taken by the motor 5 increases,its armature will draw increased current and the field 8 will increaseproportionally to the current drawn by, or the load taken up by, thearmature of the motor 5. In this manner, the output 01' the generator 5will decrease proportionately to the load taken by the motor 5. Thedynamo field I3 is arranged differentially with respect to the dynamofield I4, and it will thus be seen that the total field on the dynamo 4will increase with the decrease in output of the control generator 6 andwith the increased load taken by the armature 5. The variable controlfield I3 is so designed that itsdecreasing effect on the total field ofthe dynamo '4 will change the field characteristics of the dynamo 4 inintegrated steps from that of a motor to that of a generator withoutspeed variations of the drier rolls as the motor 5 functions to relievethe dynamo 4 of the drier motor load. This regulation can be effected insuch manner that the motor 5 through the paper 3 may take up either aportion of the power necessary to drive the drier roll set I, all ofsuch power, or more than the power necessary. In the latter case, thedynamo 4 will function as a braking generator on the drier roll set I todissipate the excess power being supplied thereto by the motor 5 throughthe coupling means provided by the tension of the paper 3.

A better understanding of the principles of this invention will be hadby a consideration of the operation of the apparatus as paper is fedthrough the roll sets I and 2 and upon subsequent breakage of the paperintermediate such roll sets..

Operation of the apparatus is initiated by energizing the direct currentbuses II--I2 and I6II and initially no paper will be contained in theroll sets I and 2. The motor 'I will be operating and will function tosupply maximum current to the control field I3, since the generatorfield 8 will be at a minimum due to the armature 5 drawing a minimum ofcurrent. The resistors i8, I9, 20 and 2! are adjusted to give the properspeed regulation of the roll sets I and 2. A strip of paper is then fedthrough the drier roll set I and thence through the calender roll set 2.As the paper is fed through the calender roll set 2, the load on themotor 5 will increase and a resultant increase in its armature currentand the current flowing through the variable generator control field 8'will be had. Increase in the field 8 will decrease the output of thegenerator 6 and thus increase the total field on the dynamo 4, therebycausing the dynamo 4 to take up less of the drier roll load or to act asa braking generator according to the desired conditions of operationwithout interfering with the speed of operation of the roll set I.

With paper being fed through the roll sets I and 2 and the paperpreceding the set 2 being under tension according to the aboveconditions, the condition which will be had upon snapping or breaking orthe paper between the sets I and 2 will now be considered. Upon suchbreakage taking place, the motor 5 will cease to transmit power to thedrier roll set I and the amount of current drawn by its armature willimmediately drop to the value prior to feeding the paper through thestack of calender rolls 2. Such drop in armature current will likewisedecrease the current flowing through the field 8 with a conwill decreasethe field of the dynamo 4 and restore to such dynamo its original motorcharactertistics causing it to act immediately to supply the powernecessary to drive the drier roll set I without any change of speed. Inthis manner the characteristics of the dynamo l are changed immediatelyto compensate for the breakage of paper, and this is done with a minimumof time delay. The rapid change of operating characteristics of thedynamo 4 is efiective to maintain the speed of operation of the drier"roll set I without any slowing down which would otherwise be effectiveto cause a loop or sag back in the paper being fed to the drier roll setI.

The control generator fields 8 and III are so I regulated that undernormal operating conditions of the roll sets I and 2 they will canceleach other, and the output of the generator 6 and value of the controlfield I3 will be zero. This usually represents the most desirableconditions of operation, but it is to be understood that the principlesof this invention are equally applicable to other arrangements oradjustments of the various control fields in which the condition doesnot exist.

It will be seen that, under the desired conditions of tension operation,current will flow in the armature circuit of the generator Ii'in asingle direction, and will vary from a maximum when the motor 5 is nottransmitting power to the drier roll set I to a minimum when the load onthe calender motor 5 and the tension in the paper 3 is at a maximum. Toprevent the flow of current in the armature circuit other than in asingle direction, a rectifier 23 of a type adapted to limit current fiowto a single direction may be inserted in the armature circuit of thegenerator Ii. The construction of the rectifier 23 forms no part per seof this invention, and accordingly has not been illustrated anddescribed in detail, the construction and operation of such rectiflersbeing well known in the art.

From the foreging, it will be seen that the control apparatus of thisinvention enables the characteristics of the dynamo 4 to be changedautomatically in accordancewith the load on the calender motor withoutany change of speed in op-' eration of the drier roll set. The load onthe calender motor being a function of the tension in the paper, it willbe seenthat the field of the dynamo 4 must be changed in accordance withsuch load as its operation changes from that of motoring tothat ofgenerating if speed is to be maintained. By utilizing theai'maturecurrent of the calender motor for regulating the generator 6 and therebythe field and operation of the dynamo 4, the necessary changes are madeto prevent speed changes such as would cause sag back.

Since certain changes may be made in the above construction anddifferent embodimentsof the invention may be made without departing fromthe scope thereof, it is intended that all the total field on saiddynamo will impart motor characteristics thereto, a direct current motorfor driving said calender rolls adapted to take up part of the load onsaid drier rolls by tensioning the paper between said -roll sets, andmeans responsive to loading of said calender drive motor for changingthe output of said generator. means to thereby increase the field ofsaid dynamo.

2, In paper making apparatus, a set of drier rolls to which a strip ofpaper is fed at a predetermined rate, a set of calender rolls to whichsaid paper is fed from said drier rolls, a dynamo mechanicallyconnectedto said drier rolls, a pair oi fields for said dynamo, aconstant source of excitation for one of said fields, a variable sourceof excitation for the other of said fields, comprising a generatorhaving a variable output, a direct current motor for driving saidcalender rolls,

and means responsive to the loading of said calender drive motor forvarying the output of said generator in such manner that the field onsaid dynamo whenfsaid motor is unloaded will impart motorcharacteristics thereto, and when the loading of said motor is increasedthe field' of said dynamo will be increased so that said dynamo willtake up less of the load and may be operated as a generator withoutspeed changes.

3. In p'aper making apparatus, a' set of drier rolls to which a strip ofpaper is fed at a predetermined rate, a set of calender rolls to whichsaid paper is fed from said drier rolls, a dynamo mechanically connectedto' said drier rolls, a pair of fields for said dynamo, a constantsource of excitation for one of said fields, a variable source ofexcitation for the other of said fields comprising a generator having. avariable output, a pair of fields for said generator, one of said gen- 7erator fields having a constant source of excitamatter contained in theabove description or shown in the accompanying drawing shall be I iorenergizing one of said fields to an extent that interpreted asillustrative and not in a limiting tion, a direct current motor fordriving said calender rolls, the other of saidgenerator fields beingconnected with the armature circuit of said calender drive motor in suchmanner that the total field on said dynamo will impart motorcharacteristics thereto for driving said drier rolls when said calendermotor is unloaded and will increase the field on said dynamo as the loadon said calender motor is increased.

4. In paper making-apparatus, a set. of drier' rolls to which a strip ofpaper is fed at a predetermined rate, a set of calender rolls to whichsaid paper is fed from said drier rolls, a dynamo mechanically connectedto said drier rolls, a direct current drive motor for driving saidcalender rolls adapted to transmit power to said drive rolls throughsaid paper, and generator means for controlling the operation of saiddynamo adapted to impart motor characteristics thereto when said drivemotor isnot transmitting power to said drier rolls through said paper;and adapted to change'the characteristics of said dynamo to enable thesame to take up less of the load of said drier rolls when said drivemotor is transmitting power to said drier rolls through said paper. p

5 In paper making apparatus, a set of drier rolls to which a strip ofpaper is fed at a predetermined rate, a set of calender rolls to which.

said paper is fed from said drier rolls, a dynamo mechanically connectedto said drier rolls, a

direct current drive motor for driving said cal- .ender rolls adapted totransmit power to said ing the output of istics thereto, and

6. In apparatus having a pair of machines for.

performing work, means coupling said machines together whereby the powerfor driving one of said machines may be supplied by the other or saidmachines, a dynamo mechanically connect.- ed to said one machine, a pairof fields for said dynamo, generator means for energizing one of saidfields to an extent that the total field on said dynamo will impartmotor characteristics thereto, a direct current motor for driving saidother machine, and means responsive to loading of said other machine forchanging the output of said generator means to thereby increase thefield of said dynamo with the loading of said motor. I

7. In apparatus having a pair of machines for performing work, meanscoupling said machines together whereby the power for driving one ofsaid machines may be supplied by the other of said machines, a dynamomechanically connected to said one machine, a pair of fields for saiddynamo, a constant source of excitation for'one of said fields, avariable source of excitation for the other of said fields comprising agenerator having excitation for the other of said fields comprising agenerator having a variable output, a pair of fields for said generator,one of said go'nerator fields having, a constant source of excitation, adirect current motor for driving said other machine, the votherofsaidgenerator fields being connected with the armature circuit of said drivemotor in such manner that the total field on said dynamo. will impartmotor characteristics thereto for driving said one machine when saidother machine is not transmitting power thereto, and will increase fieldon said dynamo so that'it may take less load without change of speedwhen said to or change the characteristics of said dynamo a variableoutput, a direct current motor for driving said other machine, and meansresponsive to the loading of said drive motor for varysaid generator insuch manner that the field on said dynamo when said drive motor isunloaded will impart motor characterwhen the loading of said motor isincreased the field of said dynamo will be increased to enablesaiddynamo to take less of the load of said one machine withoutinterfering with the speed of operation thereof.

8. In apparatus having a .pair of machines for performing work, meanscoupling said machines together whereby the power for driving one ofsaid machines may be supplied by the other of said machines, a dynamomechanically connected to said one machine, a pair of fields forsaiddynamo, a constant source of excitation for one of said fields,avariable source of so that it will supply less power without consequentspeed variations when said coupling means is operating to transmit powerfrom said other to said one machine.

10. In apparatus having a pair of machines for performingwork, meanscoupling said machines together whereby the power for driving one ofsaid machines maybe supplied by the otherof said machines, a dynamomechanically connected to said one machine, a direct current motor fordriving said other machine, a constant speed generator for controllingthe-operation of said dynamo, and means responsive to the operation ofsaid motor for controlling the output of said generator, said last namedmeans being effective to decrease'the field of said dynamo so that itwillsupply less power when said coupling means is operating to transmitpower to said one machine, and to impart motor characteristics to saiddynamo for maintaining the speed of said one machine when said couplingmeans is imperative to transmit power to said one machine. a

' WILLIAM H. FORMHALS.

